The present invention relates to a film such as a protective film for a polarizing plate, an optically anisotropic film, and the like, which is employed for a liquid crystal display, and a polarizing plate and a liquid crystal display.
In recent years, along with use of liquid crystal displays (LCD) in various types of equipment, a decrease in their thickness as well as a decrease in their weight has been demanded. Accordingly, a decrease in thickness as well as a decrease in weight is also demanded for polarizing plates employed in such LCD.
Further, along with a decrease in film thickness, problems have occurred in which, when liquid crystal displays are constructed, display unevenness tends to occur. As the results of the inventors"" investigation, it was discovered that said display unevenness is caused due to blocking, that is, films adhere to each other and the like. With a decrease in film thickness, said blocking is more likely to occur. As a result, non-uniformity of the film surface is caused due to coat mottling, crease wrinkling, and the like. Thus, said surface non-uniformity causes the display unevenness. When the wrinkling is found during transportation of the film, film breaking etc. may be caused and serious accident such as stopping production line may be induced. Such accidents become remarkable in accordance that thickness of the film becomes small as 20 to 65 xcexcm. Accordingly, in the film employed in liquid crystal displays, surface uniformity is a more essential requirement characteristic compared to films which are employed for the other purposes. The present invention relates to the enhancement of said surface uniformity of the film for liquid crystal displays.
At present, cellulose triacetate (TAC) is primarily employed as the protective film for such polarizing plate, and it is relatively thick, at least 80 xcexcm. Since four sheets of said protective film are commonly employed per plate, a decrease in its thickness is highly demanded.
However, when the thickness of TAC film, which is employed as the protective film, is decreased, during production of said TAC film as well as during the following production process of polarizing plates, problems occur such as, for example, formation of wrinkles during conveyance in the casting process, degradation of film flatness during its wound state, and the like. Thus a decrease in thickness has not been easy.
A technical object of the present invention is to obtain a cellulose ester film which exhibits excellence in handling during the film casting process as well as during the polarizing plate preparation process, when the thickness of said protective film for a polarizing plate is decreased in accordance with a decrease in thickness of liquid crystal display elements, and a production method of the same.
The invention and its embodiment are described.
(1) A film for a liquid crystal display comprising cellulose ester film and fine particles,
wherein average diameter of fine particles is 0.005 to 3.0 xcexcm, number of the fine particles per 1,000 xcexcm2 is 0 to 500 in the cross-section perpendicular to the cellulose ester film in the region of a depth of not more than 10 xcexcm, and thickness of said cellulose ester film is between 20 and 65 xcexcm.
(2) The film for a liquid crystal display of (1), wherein an amount of the fine particles in said film is 0.04 to 0.3 percent by weight with respect to cellulose ester.
(3) The film for a liquid crystal display of (1), wherein the cellulose ester film further comprises fine particles having average particle diameter of 3 to 10 xcexcm.
(4) The film for a liquid crystal display of (1), wherein haze of the cellulose ester film is 0.0 to 0.6 percent, and dynamic friction coefficient between the front surface and the back surface of said film is 0.5 to 1.3.
(5) The film for a liquid crystal display of (1), wherein the fine particles comprise a compound containing silicon atom.
(6) The film for a liquid crystal display of (1), wherein said cellulose ester film is subjected to knurling treatment of both edges so that the relationship of X (in percent)=(a/d)xc3x97100 is maintained, X is to be between 0.0 and 25.0 percent, wherein xe2x80x9caxe2x80x9d (in xcexcm) is the height of said knurling and xe2x80x9cdxe2x80x9d (in xcexcm) is the thickness of said film.
(7) The film for a liquid crystal display of (1), wherein the film is a protective layer of polarizing plate.
(8) The film for a liquid crystal display of (1), wherein A/B is 1 or more, wherein A is a number of fine particles per 1000 xcexcm2 in the region having a thickness of 10 percent of the thickness from the surface of a cellulose ester film, and B is a number of fine particles per 1000 xcexcm2 in the region having a remaining thickness of 80 percent of said thickness.
(9) The film for a liquid crystal display of (1), wherein number of the fine particles per 1,000 xcexcm2 is 0 to 5 in the cross-section perpendicular to the cellulose ester film in the region of a depth of 10 xcexcm or more
(10) The film for a liquid crystal display of (1), wherein number of projections having a size of at least 0.1 xcexcm, which exist on the surface of the cellulose ester film, is between 10 and 500 per 0.1 m2.
(11) The film for a liquid crystal display of (1), wherein true specific gravity of the fine particles is between 0.8 and 4.0.
(12) A polarizing plate comprising a first protective film for the polarizing plate, a polarizing element, and a second protective film for the polarizing plate,
wherein at least one of the first protective film and the second protective film comprises cellulose ester film and fine particles,
wherein average diameter of fine particles is 0.005 to 3.0 xcexcm, number of the fine particles per 1,000 xcexcm2 is 0 to 500 in the cross-section perpendicular to the cellulose ester film in the region of a depth of not more than 10 xcexcm, and thickness of said cellulose ester film is between 20 and 65 xcexcm.
(13) A liquid crystal display comprising first polarizing plate, a liquid crystal cell, and a second polarizing plate provided at inner portion with respect to the first polarizing plate and the liquid crystal cell, wherein
the first polarizing plate has a first polarizing element, a first protective film provided on a surface of the first polarizing element which surface is not faced to the liquid crystal cell, and a second protective film provided on a surface of the first polarizing element which surface is not faced to the liquid crystal cell,
the second polarizing plate has a second polarizing element, a third protective film provided on a surface of the second polarizing element which surface is faced to the liquid crystal cell, and a fourth protective film provided on a surface of the second polarizing element which surface is faced to the liquid crystal cell,
wherein at least one of the first protective film, the second protective film, the third protective film and the fourth protective film comprises cellulose ester film and fine particles,
wherein average diameter of fine particles is 0.005 to 3.0 xcexcm, number of the fine particles per 1, 000 xcexcm2 is 0 to 500 in the cross-section perpendicular to the cellulose ester film in the region of a depth of not more than 10 xcexcm, and thickness of said cellulose ester film is between 20 and 65 xcexcm.
(14) A preparation method of a film for a liquid crystal display comprising steps of
mixing fine particles with a dope prepared by dissolving cellulose ester in a solvent,
casting the mixture of fine particles with the dope onto a support, and
drying the cast the mixture,
wherein average diameter of fine particles is 0.005 to 3.0 xcexcm,
thickness of said cellulose ester film is between 20 and 65 xcexcm, and
the fine particles are mixed with the dope after dispersing by a high pressure homogenizer at pressure of 100 kgf/cm2 or more.
(15) A preparation method of a film for a liquid crystal display comprising steps of
mixing fine particles with a dope prepared by dissolving cellulose ester in a solvent,
casting the mixture of fine particles with the dope onto a support, and
drying the cast the mixture,
wherein average diameter of fine particles is 0.005 to 3.0 xcexcm,
thickness of said cellulose ester film is between 20 and 65 xcexcm, and
the fine particles are mixed with the dope after dispersing in a solvent at concentration of 1 to 30 wt %.
The other embodiment of the invention is described.
1. A cellulose ester film which comprises fine particles in said film in an amount of 0.04 to 0.3 percent by weight with respect to cellulose ester.
2. A cellulose ester film which comprises fine particles having an average diameter of 1.0 to 10.0 xcexcm in said film.
3. A cellulose ester film exhibiting a film haze of 0.0 to 0.6 percent as well as having a dynamic friction coefficient between the front-surface and the back surface of said film of 0.5 to 1.3.
4. The cellulose ester film described in any one of 1., 2., and 3. above, wherein the thickness of said cellulose ester film is between 20 and 65 xcexcm.
5. The cellulose ester film described in any one of 1. through 4., wherein said fine particles are comprised of a compound containing silicon atoms.
6. The cellulose ester film described in any one of 1. through 5. above, wherein said cellulose ester film is subjected to knurling treatment of both edges so that when the relationship of X (in percent)=(a/d)xc3x97100 is maintained, X is to be between 0.0 and 25.0 percent, wherein xe2x80x9caxe2x80x9d (in xcexcm) is the height of said knurling and xe2x80x9cdxe2x80x9d (in xcexcm) is the thickness of said film.
7. A protective film for a polarizing plate which is prepared employing the cellulose ester film described in any one of 1. through 6. above.
8. A production method of a cellulose ester film wherein after dispensing fine particles at a pressure of at least 100 kgf/cm2 employing a high pressure homogenizer, the resultant dispersion is blended with a dope prepared by dissolving cellulose ester in a solvent, and the resultant blend is cast onto a support and subsequently dried.
9. A production method of a cellulose ester film wherein after dispensing fine particles in a solvent comprising lower alcohols in an amount of 25 to 100 percent by weight, the resultant dispersion is blended with a dope prepared by dissolving cellulose ester in a solvent, and the resultant blend is cast onto a support and subsequently dried.
10. A production method of a cellulose ester film wherein after dispensing fine particles in a solvent to obtain a concentration of 1 to 30 percent by weight, the resultant dispersion is blended with a dope prepared by dissolving cellulose ester in a solvent, and the resultant blend is cast onto a support and subsequently dried.
11. The production method of a cellulose ester film described in any one of 8., 9., and 10. above wherein the thickness of said cellulose ester film is between 20 and 65 xcexc.